Electric machines such as, for example, motors and generators may be used to generate mechanical power in response to an electrical input or to generate electrical power in response to a mechanical input. Magnetic, resistive, and mechanical losses within the motors and generators during mechanical and electrical power generation cause a build up of heat, which may be dissipated to avoid malfunction and/or failure of the electric machine. One of the limitations on the power output of the electric machines may be the capacity of the electric machine to dissipate this heat.
One method of dissipating heat within a generator includes directing a cooling medium into the generator via a rotor. For example, U.S. Pat. No. 5,019,733 (the '733 patent) to Kano et al. teaches an excitation-type AC generator having stator and field coils cooled by a fluid passing through the rotating shaft of a rotor. Specifically, during circulation, the fluid is directed axially into one end of the rotor shaft and then immediately outward via radially-bored passageways to spray the fluid onto the stator and field coils, thereby removing heat from the generator.
Although the radially-bored passageways of the rotor shaft may facilitate some heat removal from portions of the excitation-type AC generator, they may remove too little heat, and the removal of heat may be disproportionate. In particular, because the cooling fluid of the '733 patent is directed away from the rotor immediately after entering the rotor, it may be ineffective for removing substantial amounts of heat from the rotor. In addition, because the fluid enters the rotor shaft from only one end and then is immediately redirected away from the rotor, little or no heat may be removed from the other end of the rotor. This insufficient and disproportionate heat removal could be damaging to components of the generator.
The disclosed electric machine is directed to overcoming one or more of the problems set forth above.